1. Field of the Invention
The invention relates in general to elevator systems, and more specifically to elevator systems which generate distance pulses in response to movement of the elevator car.
2. Description of the Prior Art
An elevator system requires a normal terminal stopping arrangement which, independently of the normal slowdown and stopping arrangement, will automatically reduce the speed of the elevator car as it approaches a terminal landing, and stop it at the terminal floor. The independent terminal slowdown function will hereinafter be referred to as TSD, for "Terminal Slow Down". Also, some additional emergency terminal device must be used. For example, with reduced stroke buffers, an emergency terminal speed limiting device must be used which is completely independent of any other emergency-related device. This same terminal speed limiting device may also be used in elevator systems which have normal stroke buffers. This device will hereinafter be referred to as ETS for "Emergency Terminal Stop".
With solid state elevator control systems, it is convenient to keep track of car position by generating a distance pulse for each predetermined standard increment of car movement, such as a distance pulse for each 0.25 inch of car travel, and to increment or decrement a car position counter according to travel direction. The distance pulses may also be used in the generation of the normal slowdown and stopping speed pattern. The normal slowdown and stopping arrangement will be referred to as SLDN.
One prior art arrangement for providing ETS utilizes hatch switches and speed switches in the form of mercury switches located on the governor. The mercury switches have the disadvantage of a substantial tolerance in the speed setting.
In distance pulse speed pattern systems, it is not permissible to develop TSD from the distance pulses, as TSD must be completely independent of SLDN. The distance pulses may be used in the ETS function, however, as long as they are not used in any other emergency related device. Thus, it would be desirable to provide a new and improved ETS arrangement utilizing the distance pulses.